Agent
Chemical structure
Anion
Cation
% Salt concentration
% Iodine concentration
Iodine mg/ml
Viscosity 25 °C
Viscosity 37 °C
Osmolality mOsm/kg H2O
Visipaque™ 270 (GE Healthcare)
Iodixanol
Nonionic
Nonionic
None
27
270
12.7
6.3
290
Isovue™ 300 (Bracco)
Iopamidol 61.2%
Nonionic
Nonionic
None
30
300
8.8
4.7
616
Omnipaque ™ 300 (GE Healthcare)
Iohexol 64.7%
Nonionic
Nonionic
None
30
300
11.8
6.3
672
Optiray™ 300 (Mallinckrodt inc)
Ioversol
64%
Nonionic
Nonionic
None
30
300
8.2
5.5
651
Optiray™ 320 (Mallinckrodt inc)
Ioversol 68%
Nonionic
Nonionic
None
32
320
9.9
5.8
702
While usually high-osmolality contrast media (HOCM) are safe and effective and these agents cost less, if possible these should be avoided in patients at higher risk, e.g., patients with CHF, renal insufficiency, diabetes. HOCM will typically cause more discomfort for the patient on injection. HOCM include very hypertonic monomers, e.g., 1500 mOsm/kg for 300 mgI2/ml.
Low-osmolality contrast media (LOCM) are relatively more expensive and cause less discomfort and minor (1% vs 5%) or major (0.015% vs 0.1%) adverse reactions. Most LOCM are nonionic, e.g., 300 mOsm/kg for 300 mgI2/ml.
Some centers use LOCM exclusively, while others use it in patients at high risk. High-risk patients include:
History of adverse reaction to iodine-containing contrast agents (sensation of warmth, flushing, or a single episode of nausea/vomiting is not considered adverse reactions).
History of serious allergic reaction to materials other than contrast agents.
Severe arrhythmia, unstable angina or, recent MI.
Renal insufficiency, especially in the presence of diabetes.
General severe debilitation, etc.
Adverse Effects
The pathogenesis of adverse effects may be multifactorial. The etiology may include:
Specific chemical formulation of the contrast (chemotoxicity).
Hypertonicity.
Binding of small contrast agents in the blood to activators.
Ca-chelating substances.
Substances leeched from rubber stoppers in bottles or syringes.
Patient anxiety.
A previous h/o adverse event to contrast injection is the best predictor of recurrent event. Recurrent events occur in 8–30% patients.
Adverse events include the following (Table 4.2).
Table 4.2
Adverse events
Adverse event
Comment
Urticaria
Due to histamine release, usually urticaria and other allergic reactions are more likely to occur in patients with a h/o allergic reactions
Bronchospasm
More likely in patients with h/o asthma
Acute pulmonary edema
Prone to occur in patients with left HF who are less able to compensate for negative chronotropic events associated with contrast agents. Use LOCM in such patients
Hemodynamic changes
More likely in patients with severe cardiovascular disease, e.g., aortic stenosis or, severe CHF
Hypotension/tachycardia
May be consequent to the hypertonicity of the agent
Vasovagal reaction
Due to increased vagal tone, which causes decreased SA and AV nodal activity, decreased AV conduction and peripheral vasodilatation. The result is hypotension and bradycardia. The vasovagal reaction may be consequent to anxiety and therefore may occur during taking consent, or placing needle, or injecting contrast. It is usually mild and self-limiting. However, if it is not monitored or treated, it may progress to hemodynamic collapseRelated posts:
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